Apollo, son of Zeus and the Titan Leto, is, after Hera and his father, the greatest power in the pantheon. Though both Poseidon and Hades are stronger, Apollo commands more respect than either of them, and thus is next in line should Zeus ever perish or pass on.
As a god of prophecy, Apollo founded an oracle on every prime-material world the Olympians have influence. They all sit on stools in smoke-filled caverns, listening to the words of the future breathed by the fumes. Like most oracles, they speak in words that're usually understood by mortals only after the prophecy fulfils itself. Apollo's also established a site on Mount Olympus; those in need of the power's advice can seek out the mysterious oracle Pythia.
Apollo's temple is also his home, and the whole place is fashioned of beaten gold that shines eternally with the mellow glow of the sun. It the back of the temple, he's built an amphitheatre where the finest playwrights of the culture enact their works. Mortal poets also pad the stage, declaiming verse to honor the Light-bringer.
Asclepius the Healer is Apollo's son, and also one of his proxies. It's said that the blood can bring the dead back without benefit of spells. Hades, of course, wants this stopped, and unless Apollo steps in, he's likely to lose his child to the jealous death god. Another well-known proxy is Cyparissus, whose companion is a stag; the two of them can communicate with any natural animal in the multiverse.